My proceessor tops at 28%

I have an XPS 9560 with a 2.8 GHz processor (i7 7th gen 4core)

Windows performance tab in the task manager is showing my CPU at 0.78 GHz and when I make the processor work hard, it tops at 28%...

I went to BIOS to reset to factory settings just in case but it didn't change a thing..